1. Field of the Invention
The present invention is related to a rotary combustor, or incinerator, for burning waste material and, more particularly, to an improvement in the water-cooled barrel used in such a rotary combustor.
2. Description of the Related Art
Proper disposal of solid waste has become an increasingly serious problem as existing sites for land disposal near capacity and new sites become increasingly difficult to locate. Incineration of combustible solid waste has long been used to reduce the quantity of solid matter needing disposal. However, older methods of incineration often resulted in incomplete combustion and were often wasteful, in that the heat generated from combustion was rarely used efficiently.
During the previous one to two decades, a device, known as a water-cooled rotary combustor, has been used increasingly to burn waste materials efficiently with the heat energy therefrom producing steam for use in generating electricity or for other industrial uses. Examples of rotary combustors are described in U.S. Pat. Nos. 3,822,651 to Harris et al.; 4,066,024 to O'Connor and 4,226,584 to Ishikawa. A general description of a rotary combustor is provided immediately below with reference to FIGS. 1A and 2A which illustrate the present invention as applied to a prior art combustor. A more detailed description will be provided later.
As illustrated schematically in a cross-sectional side elevational view in FIG. 1A, a water-cooled rotary combustor generally includes a combustion barrel 10 having a generally cylindrical side wall 30 affixed to annular support bands 35 which are received on rollers 12 to permit rotation about the longitudinal axis. The barrel 10 has a generally open input end 16 for receiving waste 14 and an exit end 18 from which heat (or flame) 20 and solid combustion products 22, i.e., ash, exit the barrel 10. Cooling of the barrel 10 is provided by cooling pipes 24 which form a substantial portion of the generally cylindrical side wall 30 of the barrel 10. Low-energy coolant, such as saturated water, is supplied via supply pipes 26 to the barrel 10 at the exit end 18 and high-energy coolant is discharged via the supply pipes 26 to heat exchanging equipment 27. The heat exchanging equipment reduces the heat energy in the coolant before it is returned to the barrel 10 by a pump 29.
As illustrated in FIG. 2A, the barrel 10 rotates in, e.g., a clockwise direction when viewed from the flue 28, at a slow rate, such as one-sixth rpm. As a result of the barrel's rotation, the waste material 14 is shifted to one side of the barrel 10, as it travels a spiral path downward from the input end 16 to the exit end 18. However, the barrel 10 typically rotates at such a slow rate that some material often remains on the bottom for a significant portion of its travel down the length of the combustion barrel 10.
As a result, a portion of the waste material 14 is not exposed to a sufficient amount of heat and air to be fully incinerated. When this occurs, the solid combustion products 22 exiting the exit end 18 of the combustion barrel 10 include not only ash, but also chunks of material which may be charred, but still retain a significant amount of their original mass. Since one of the objectives of using a rotary combustor is to minimize the quantity of material which is to be disposed, the output of unburned material from the combustion barrel 10 is undesirable.
U.S. Pat. No. 4,066,024 to O'Connor describes one attempt in the prior art to increase agitation of material inside a combustion barrel. The O'Connor '024 patent is directed to a fluidized bed rotary combustor containing heated sand in the combustion barrel. Curved fins are attached to the interior surface of the combustion barrel to transport a portion of the sand to the top of the combustion barrel to provide more even heating of the sand. The fins are attached to air ducts having openings which help increase the air flow through the sand above that which would be provided by a conventional rotary combustor. Since the fins and air ducts are not water-cooled, they must be formed of materials which are capable of withstanding higher temperatures than the temperatures to which the carbon steel cooling pipes 24 are subjected.